1. Field of the Invention
The present invention relates to a hydraulic control device for an automatic transmission for a vehicle such as an automobile, and more particularly, to a hydraulic control device for an automatic transmission for a vehicle such as an automobile including a speed stage shifting device having a hydraulically operated friction engaging means such as a clutch adapted to be engaged when a first speed stage and a second speed stage are set up and disengaged when a third speed stage is set up, the engagement of said friction engaging means being essential for setting up said first speed stage while the engagement of said friction engaging means is not essential for setting up said second speed stage unless engine brake availability is required.
2. Description of the Prior Art
In Japanese Patent Application 62-195471 filed on Aug. 5, 1987 and laid open to public on Feb. 13, 1989, two of the inventors of the present invention have proposed an automatic transmission for a vehicle such as an automobile in which the speed stage shifting device has a hydraulically operated friction engaging means such as described above.
In more detail, in an embodiment of the automatic transmission proposed by the above-mentioned Japanese patent application, as shown in Table 1 and FIG. 2 of the present application, a first clutch C.sub.1 is engaged when the so-called 1st speed stage, 2nd speed stage and 3rd speed stage are set up and is disengaged when the 4th speed stage is set up. In the 2nd speed stage it is essential that the clutch C.sub.1 is engaged, but in the 3rd speed stage it is not essential that the clutch C1 is engaged unless engine brake availability is required since a one way clutch F.sub.1 is provided in parallel with the clutch C.sub.1. Therefore, in setting up the 2nd speed stage, particularly in downshifting to the 2nd speed stage from the 4th speed stage in which the clutch C.sub.1 is disengaged, it is necessary that the clutch C.sub.1 is relatively quickly engaged, while in setting up the 3rd speed stage, including in downshifting from the 4th speed stage in which the clutch C.sub.1 is disengaged, it is not necessary that the clutch C.sub.1 is quickly engaged or rather it is desirable that the clutch C.sub.1 is engaged with a substantial delay so as not to cause any temporary engine braking to occur.